Aqueous system containing a synergistic phosphonate scale control combination

ABSTRACT

An aqueous system containing scale forming salts including both calcium carbonate and calcium phosphate and characterized by high pH and high calcite concentrations which further contains a synergistic effective amount of a combination comprising (A) a polyether polyamino methylene phosphonate, (B) a terpolymer comprising the monomers of acrylic acid, sulfophenomethallyl ether and maleic acid, and (C) a hydroxyphosphonoacetic acid, is disclosed. A method for inhibiting the formation, deposition and adherence of such scale forming salts in the aqueous system employing the synergistic combination is also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a synergistic combination comprising apolyether polyamino methylene phosphonate, a terpolymer comprising themonomers of acrylic acid, sulfophenomethallyl ether and maleic acid, andhydroxyphosphonoacetic acid for controlling the deposition of calciumcarbonate and calcium phosphate scale deposits on the surfaces of anaqueous system.

2. Brief Description of the Background Art

Generally, calcium carbonate and calcium phosphate scale deposits areincrustation coatings which accumulate on the metallic or plasticsurfaces of a water-carrying system through a number of differentcauses.

Various industrial and commercial water-carrying systems are subject tocalcium carbonate and calcium phosphate scale formation problems.Calcium carbonate and calcium phosphate scales are of particular concernin heat exchange systems employing water, such as, for example, boilersystems and once-through and open recirculating water cooling systems.Cooling towers are especially significant, particularly where severeconditions including high pH and high calcite concentrations areencountered.

The water employed in these systems ordinarily will contain a number ofdissolved salts, and the alkaline earth metal cation calcium is usuallyprevalent, as are the anions carbonate and phosphate. The combinationproducts of calcium cation and carbonate anion and calcium cation andphosphate anion will precipitate from the water in which the ions arecarried to form scale deposits when the concentrations of the anion andcation comprising the reaction product, i.e., calcium carbonate, orcalcium phosphate, exceeds the solubility of the reaction productitself. Thus, when the concentration of calcium ion and anion exceed thesolubility of the calcium reaction product, a solid phase of calciumcarbonate and/or calcium phosphate will form as a precipitate.Precipitation of the reaction product will continue until the solubilityproduct concentration of the constituent ions is no longer exceeded.

Numerous factors may be responsible for producing a condition ofsupersaturation for the reaction product. Among such factors are changesin the pH of the water system, evaporation of the water phase, rate ofheat transfer, amount of dissolved solids, and changes in thetemperature or pressure of the system.

For cooling systems and similar heat exchange systems, including coolingtowers, the mechanism of scale formation is apparently one ofcrystallization of scale-forming salts from a solution which is locallysupersaturated in the region adjacent the heating surface of the system.The thin viscous film of water in this region tends to become moreconcentrated than the remainder of the solution outside this region.Precipitation is also favored on the heat transfer surface because ofthe inverse solubility relationship of calcium carbonate. As a result,the solubility of the scale-forming calcium carbonate salt reactionproduct is first exceeded in this thin film, and crystallization ofcalcium carbonate scale results directly on the heating or heat exchangesurface.

In addition to this, a common source of scale in boiler systems is thebreakdown of calcium bicarbonate to form calcium carbonate, water andcarbon dioxide under the influence of heat. For open recirculatingcooling water systems, in which a cooling tower, spray pond, evaporativecondenser, and the like serve to dissipate heat by evaporation of water,the chief factor which promotes calcium carbonate scale formation isconcentration of solids dissolved in the water by repeated evaporationof portions of the water phase. Thus, even a water which is not scaleforming on a once-through basis usually will become scale forming whenconcentrated two, four or six times. Moreover, alkalinity of the make-upwater, with evaporative cycles over time results in an increasingalkalinity of the water in the overall system, often having pH's of8.5-9.5 and even higher. Conventional scale inhibiting compositionstypically fail in systems having such severe conditions.

The formation of calcium carbonate and calcium phosphate scale depositsposes a serious problem in a number of regards. The calcium scale whichis formed possesses a low degree of heat conductivity. Thus, a calciumscale deposit is essentially an insulating layer imposed across the pathof heat travel from whatever source to the water of the system. In thecase of a cooling system, the retarded heat transfer causes a loss incooling efficiency. Consequently, calcium scale is an expensive problemin many industrial water systems, causing delays and shutdowns forcleaning and removal.

Although the present invention is directed primarily to preventing orinhibiting the deposition of calcium carbonate and calcium phosphatescale, it is also applicable to inhibiting the deposition of other typesof alkaline earth metal scales, especially those associated with calciumcarbonate scale under the severe conditions described herein. Forexample, most industrial and commercial water contains alkaline earthmetal cations, such as calcium and magnesium, etc., and several anionssuch as bicarbonate, carbonate, and phosphate. When combinations ofthese anions and cations are present in concentrations which exceed thesolubility of their reaction products, precipitates form until theirproduct solubility concentrations are no longer exceeded. Theseprecipitates are alkaline earth metal scales. Thus, by alkaline earthmetal scales is meant scales including but not limited to calciumcarbonate, calcium phosphate and magnesium carbonate. These scales formfrequently in the tubes of heat exchangers and on other heat exchangesurfaces, such as those in cooling towers. Particular systems orapplications areas where severe conditions lead to exceptional buildupof calcium carbonate and calcium phosphate scales, in addition to cycledup cooling towers, include reverse osmosis systems, sugar refiningevaporators and certain types of gas scrubbers.

The synergistic combination of the present invention is used in amountsas threshold inhibitors to achieve calcium scale inhibition, rather thansequestering or chelating agents, although the combination of thepresent invention has dispersant properties as well and significantlyreduces the adherency of any scale deposit which is formed, facilitatingits easy removal.

Scale-forming compounds can be prevented from precipitating byinactivating their cations with chelating or sequestering agents, sothat the solubility of their reaction products is not exceeded.Generally, this requires many times as much chelating or sequesteringagent as cation, since chelation is a stoichiometric reaction; theseamounts are not always desirable or economical. However, several decadesago, it was discovered that certain inorganic polyphosphates wouldprevent such precipitation when added in amounts far less than theconcentrations needed for sequestering or chelating.

When a precipitation inhibitor is present in a potentially scale-formingaqueous system at a markedly lower concentration than that required forsequestering the scale-forming cation (stoichiometric), it is said to bepresent in "threshold" amounts. See, for example, Hatch and Rice,Indust. Eng. Chem. 31, 51-53 (1939); Reitemeier and Buehrer, J. Phys.Chem., 44(5), 535-536 (1940); Fink and Richardson, U.S. Pat. No.2,358,222; and Hatch, U.S. Pat. No. 2,539,305.

Similarly, anionic and cationic polymers can be used as dispersants inaccordance with methods known in the art, but the dosage levelsnecessary to achieve dispersion are in the range of 0.5-1.0% by weightof the aqueous system being treated, which is many orders of magnitudehigher than the dosage levels used for the combination of the presentinvention. Thus, it is a unique aspect of the present invention that itis possible to achieve essentially non-adherent scale using onlythreshold inhibitor dosage levels of the synergistic combinations of thepresent invention.

Recently, attention has been focused on controlling scaling under severeconditions, where conventional treatments such as those described abovedo not provide complete scale control for calcium carbonate and calciumphosphate. Current technology in scale control can be used to inhibitCaCO₃ scale up to 100 to 120 times calcite saturation, i.e., a watercontaining Ca²⁺ and CO₃ ²⁻ present at 100 times (100×) the solubilitylimit of calcium as calcite (calcite is the most common crystalline formof calcium carbonate). However, what is desired are inhibitors effectivein greater than 100× water, where the calcite ions can be prevented fromprecipitating as calcium carbonate scale and also wherein the inhibitorsare effective in inhibiting the formation of calcium phosphate scale aswell, using substoichiometric amounts of an inhibitor. Further, thesynergistic combinations of the present invention are especially usefulunder severe conditions characterized by a calcite saturation level ofgreater than 150× as defined in the paragraph immediately below, for thecontrol of both calcium carbonate and calcium phosphate scales.

Severity of the scaling tendency of a water sample is measured using thesaturation index, which may be derived in accordance with the followingequation: ##EQU1## where SI is the saturation index for calciumcarbonate, Ca²⁻ ! is the concentration of free calcium ions, CO₃ ²⁻ ! isthe concentration of free carbonate ions, CO₃ ²⁻ ! is the concentrationof free carbonate ions, and K_(sp) CaCO₃ is the conditional solubilityproduct constant for CaCO₃. All of the quantities on the right side ofthe above equation are adjusted for pH, temperature and ionic strength.

Calculation and use of the saturation index, and generation of the datafrom which it is derived, are matters within the skill of the art. See,for example, Critical Stability Constants, Vol. 4: "InorganicComplexes", Smith & Mantell (1976), Plenum Press; and Aquatic Chemistry,Chap. 5, 2nd ed., Stumm a Morgan (1981), Wiley & Sons.

Another characteristic feature of the severe conditions under which thescale controlling methods of the present invention are especially usefulis high pH, greater than about 8.5. A related feature of such severeconditions is high alkalinity.

One of the particular advantages of the scale inhibiting combinations ofthe present invention is the exceptional calcium tolerances which theyexhibit. Calcium tolerance is a measure of a chemical compound's abilityto remain soluble in the presence of calcium ions (Ca²⁺ !. One of theparameters of scale control under severe conditions is pH. As pHincreases, calcium tolerance decreases rapidly for traditional CaCO₃threshold inhibitors, e.g., 1-hydroxyethylidene-1,1-diphosphonic acid(HEDP) and amino tri(methylene phosphonic acid) (AMP). These inhibitorsprecipitate with calcium at alkaline pH's, rendering them useless asthreshold scale inhibitors.

Early efforts to reduce scale formation in water-carrying systemsemployed compounds such as tannins, modified lignins, algins, and othersimilar materials. Chelating or sequestering agents have also beenemployed to prevent precipitation or crystallization of scale-formingcalcium carbonate. Another type of agent which has been activelyexplored heretobefore as a calcium carbonate scale inhibiting materialis the threshold active inhibitor. Such materials are effective as scaleinhibitors in amounts considerably less than stoichiometricallyrequired, and this amount, as already mentioned, is termed the thresholdamount. Inorganic polyphosphates have long been used as such thresholdactive inhibitors. For examples of such materials, see Fink--U.S. Pat.No. 2,358,222; Hatch--U.S. Pat. No. 2,539,305; and Ralston--U.S. Pat.No. 3,434,969. Certain water soluble polymers, including groups derivedfrom acrylamide and acrylic acid have been used to condition watercontaining scale-forming calcium carbonate. For example, See U.S. Pat.Nos. 2,783,200; 3,514,476; 2,980,610; 3,285,886; 3,463,730; 3,518,204;3,928,196; 3,965,027; and 4,936,987. In particular, there has beenemployed anionic polyelectrolytes such as polyacrylates, polymaleicanhydrides, copolymers of acrylates and sulfonates, and polymers ofsulfonated styrenes. See, for example, U.S. Pat. No. 4,640,793;4,650,591; 4,457,847; and 4,671,888. However, when used as thresholdalkaline earth metal scale inhibitors, large dosages of these polymersare required, which in turn increases operating costs.

While polyether polyamino methylene phosphonates of the type thatcomprises one element of the synergistic combination of the instantinvention, are known for their use for the control of alkaline earthmetal scale having severe conditions wherein the pH is at least 8.5 andthe calcite saturation is at least 150 times the solubility limit ofcalcium as calcite, U.S. Pat. Nos. 5,338,477 and 5,358,642, the aqueoussystem having the synergistic combination of the instant invention hasnot heretobefore been suggested. Further, as demonstrated herein, use ofthe polyether polyamino methylene phosphonates alone for the control ofalkaline earth metal scales such as calcium carbonate and calciumphosphate simultaneously require large dosages making the use of thepolyether polyamino methylene phosphonate alone expensive and thereforeincreasing operating costs to an unacceptable level.

In spite of this background material, there remains a very real andsubstantial need for a synergistic combination and a method ofinhibiting the formation, deposition and adherence of scale formingsalts in an aqueous system, such as for example, but not limited to, acooling tower.

SUMMARY OF THE INVENTION

The present invention has met the above-described needs. The presentinvention relates to an aqueous system containing scale forming saltsand characterized by high pH and high calcite concentrations wherein thepH is at least 8.5 and the calcite saturation level is at least 100times the solubility limit of calcium as calcite, which further containsa synergistic effective amount of a combination comprising: (A) apolyether polyamino methylene phosphonate of the formula: ##STR1## wheren is an integer or fractional integer which is, or on average is, fromabout 2 to about 12, inclusive; M is hydrogen or a cation of an alkalimetal salt; and each R may be the same or different and is independentlyselected from hydrogen and methyl; (B) a terpolymer comprising themonomers of acrylic acid, sulfophenomethallyl ether and maleic acid,wherein the weight average molecular weight for said terpolymer is inthe range from about 4,000 to 10,000; and (C) a hydroxyphosphonoaceticacid. Preferably, the combination includes wherein for the polyetherpolyamino methylene phosphonate, M is hydrogen, each R is methyl, and nis about 2 to 4, and more preferably wherein n is an average of about2.6. The aqueous system of the present invention as described hereinincludes wherein the weight ratio of (A) polyether polyamino methylenephosphonate: (B) terpolymer: (C) hydroxyphosphonoacetic acid ranges fromabout 1:2:1 to about 5:2:1.

In a preferred embodiment of this invention, the aqueous system asdescribed herein is provided wherein the terpolymer (B) is about 84weight average molecular weight percent acrylic acid, about 8.0 weightaverage molecular weight percent sulfophenomethallyl ether, and about8.0 weight average molecular weight percent maleic acid.

In another embodiment of this invention, the aqueous system as describedherein is provided wherein the aqueous system additionally includes astabilizer for preventing decomposition of the (A) polyether polyaminomethylene phosphonate.

In yet another embodiment of this invention, the aqueous system asdescribed herein is provided wherein the aqueous system additionallyincludes a corrosion inhibitor. The corrosion inhibitor is, such as forexample, but not limited to a steel and/or copper corrosioninhibitor(s). Another embodiment of this invention, provides an aqueoussystem containing scale forming salts and characterized by high pH andhigh calcite concentrations wherein the pH is at least 8.5 and thecalcite saturation level is at least 100 times the solubility limit ofcalcium as calcite, which further contains a synergistic effectiveamount of a combination comprising: (A) a polyether polyamino methylenephosphonate of the formula: ##STR2## where n is an integer or fractionalinteger which is, or on average is, from about 2 to about 12, inclusive;M is hydrogen or a cation of an alkali metal salt; and each R may be thesame or different and is independently selected from hydrogen andmethyl; (B) a composition comprising a mixture of polymaleic acid and acopolymer of acrylic acid and sulfophenomethallyl ether wherein theweight ratio of acrylic acid: sulfophenomethallyl ether of saidcopolymer ranges from about 3:1 to 18:1, and wherein said compositionhas a weight average molecular weight ranging from about 4,000 to10,000; and (C) a hydroxyphosphonoacetic acid.

In yet another embodiment of this invention a method is provided forinhibiting the formation, deposition and adherence of scale formingsalts in an aqueous system having a pH of at least 8.5 and a calcitesaturation level of at least 100 times the solubility limit of calciumas calcite, comprising adding to said aqueous system an effectivesynergistic amount of a combination of (A) an amount to establish aconcentration of at least about 1.0 mg/L, of the formula: ##STR3## wheren is an integer or fractional integer which is, or on average is, fromabout 2 to about 12, inclusive; M is hydrogen or a cation of an alkalimetal salt; and each R may be the same or different and is independentlyselected from hydrogen and methyl; (B) an amount sufficient to establisha concentration of at least about 2.0 mg/L of a terpolymer comprisingthe monomers of acrylic acid, sulfophenomethallyl ether and maleic acid,wherein said terpolymer has a weight average molecular weight in therange from about 4,000 to 10,000; and (C) an amount sufficient toestablish a concentration of at least about 1.0 mg/L of ahydroxyphosphonoacetic acid.

In a preferred embodiment of this invention, the method as describedherein includes adding a stabilizer to the aqueous system as describedherein.

In another preferred embodiment of this invention, the method asdescribed herein includes adding at least one corrosion inhibitor to theaqueous system as described herein.

Another embodiment of this invention provides a method of inhibiting theformation, deposition and adherence of scale forming salts in an aqueoussystem having a pH of at least 8.5 and a calcite saturation level of atleast 100 times the solubility limit of calcium as calcite, comprisingadding to said aqueous system an effective synergistic amount of acombination of (A) an amount to establish a concentration of at leastabout 1.0 mg/L, of the formula: ##STR4## wherein n is an integer orfractional integer which is, or on average is, from about 2 to about 12,inclusive; M is hydrogen or a cation of an alkali metal salt; and each Rmay be the same or different and is independently selected from hydrogenand methyl; (B) an amount sufficient to establish a concentration of atleast 2.0 mg/L of a composition comprising a mixture of polymaleic acidand a copolymer of acrylic acid and sulfophenomethallyl ether whereinthe weight of acrylic acid:sulfophenomethallyl ether of said copolymerranges from about 3:1 to 18:1, and wherein said composition has a weightaverage molecular weight ranging from about 4,000 to 10,000; and (C) anamount sufficient to establish a concentration of at least about 1.0mg/L of a hydroxyphosphonoacetic acid. Another embodiment of thisinvention provides the method as described herein which further includesadding one or both of a stabilizer to the aqueous system for preventingdecomposition of the polyether polyamino methylene phosphonate and atleast one corrosion inhibitor.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention is directed to an aqueous system containing scaleforming salts and a synergistic effective amount of a combination as setforth herein, and a method of inhibiting the formation, deposition, andadherence of scale forming salts in the aqueous system.

As used herein the phrases "inhibiting the precipitation" and"inhibiting the deposition" include threshold inhibition, dispersion,solubilization, or particle size reduction. The phrase "inhibiting theadherence" and "increasing the non-adherence", define the formation of ascale deposit which is easily removed, e.g., by simple rinsing, i.e., ascale deposit which is not so firmly bonded to the surface to which itis attached that it cannot be removed by simple physical means asopposed to harsh mechanical or chemical treatment.

As used herein, the phrase "scale-forming salts" includes any of thescale-forming salts, including, but not limited to, calcium carbonate,calcium sulfate, calcium phosphate, calcium phosphonate (includingcalcium hydroxyethylidene diphosphonic acid), calcium oxalate, calciumfluoride, barium sulfate and magnesium salts.

As used herein, the phrase "aqueous system" refers to commercial orindustrial system utilizing water and involving heat exchange surfaces,usually of metal, including, but not limited to, cooling water systems,especially cooling towers, boiler water systems, desalination systems,gas scrubbers and thermal conditioning equipment. Of particularimportance are those systems which operate under severe conditions asdetailed herein, including high pH and high calcite concentrations.Typical of such systems are cycled up cooling towers, reverse osmosissystems, sugar refining evaporators and gas scrubbers.

The present invention provides an aqueous system containing scaleforming salts and characterized by high pH and high calciteconcentrations wherein the pH is at least 8.5 and the calcite saturationlevel is at least 100 times the solubility limit of calcium as calcite,which further contains a synergistic effective amount of a combinationcomprising: (A) a polyether polyamino methylene phosphonate of theformula: ##STR5## where n is an integer or fractional integer which is,or on average is, from about 2 to about 12, inclusive; M is hydrogen ora cation of an alkali metal salt; and each R may be the same ordifferent and is independently selected from hydrogen and methyl; (B) aterpolymer comprising the monomers of acrylic acid, sulfophenomethallylether and maleic acid, wherein the weight average molecular weight forsaid terpolymer is in the range from about 4,000 to 10,000; and (C) ahydroxyphosphonoacetic acid.

Preferably, the aqueous system includes wherein for the (A) polyetherpolyamino methylene phosphonate of the formula described hereinabove,the M is hydrogen, R is methyl, and n is from about 2 to 3, and mostpreferably an average of about 2.6.

In order to obtain high levels of control of scale deposits, especiallyunder the severe conditions defined herein, it has been found that thereare certain essential components of the structure of the polyetherpolyamino methylene phosphonate (A) of the present invention which arenecessary to provide that performance. Thus, e.g., thetetra(aminophosphonate) portion of the structure is essential. Whetherthese groups are present initially in the phosphonic acid form or as analkali metal or other salt of the acid, has no real bearing on theperformance of the overall molecule. At the pH's under which thecompositions of the present invention function, they are, and must be,in their ionized form. Thus, it is not critical whether "M" is hydrogenor a suitable cation, and the selection of an appropriate salt form iswell within the skill of the art. In addition to alkali metal salts,ammonium salts: NH₄ ⁺, or ammonium derivative salts: NR₄ ⁺ (R=alkyletc.), or mixtures thereof, may be used. Alkali metal salts are the mostsimple, and are preferred for that reason.

A desirable, although not essential structural feature of the (A)polyether polyamino methylene phosphonates useful in the aqueous systemand methods of the present invention is the isopropyl group whichbridges the diphosphonomethylamino group and the polyether group:##STR6## The isopropyl group has been found to provide enhanced scaleinhibition activity under the severe conditions defined herein.

The next structural element of the polyether polyamino phosphonates tobe considered is the polyether moiety: ##STR7## R may be hydrogen ormethyl, and thus the polyether moiety is either polyoxyethylene orpolyoxypropylene, with the polyoxypropylene being preferred. Since thepolyether polyamino methylene phosphonates are prepared byphosphonomethylation of the appropriate diamine, the character of thepolyether moiety will depend upon the way in which the amine startingmaterial is made. Processes for making such polyether diamines are knownin the art; and attention is directed particularly to U.S. Pat. No.3,236,895, which describes preparation of a variety of polyetherdiamines especially useful in preparing the phosphonate final products(A), as described herein, used in synergistic combination as depositcontrol agents in the present invention.

In accordance with the processes set out in U.S. Pat. No. 3,236,895 andrelated processes described in the prior art, it is possible to prepareany one of a number of desired polyether diamines within the scope ofthe present invention. In the general formula for the (A) polyetherpolyamino methylene phosphonates used herein, the polyether moiety issimply represented by the formula above. Since R may be hydrogen ormethyl, both ethyleneoxy and propyleneoxy units are possible, as alreadymentioned. Moreover, R is to be independently chosen, i.e., ethyleneoxyand propyleneoxy units may alternate in various patterns, includingblocks of each, or they may be all one or the other. For example, thefollowing are just some of the polyether segments which might beprepared to form the basis for the corresponding diamines, which wouldthen be used to make phosphonates within the scope of the presentinvention (where EO=ethyleneoxy, and PO=propyleneoxy):

EO:PO; EO-EO; PO-PO; EO-PO; EO-EO-EO;

PO-PO-PO; EO-EO-PO; EO-PO-PO; EO-PO-EO;

PO-EO-PO; EO-EO-EO-EO; PO-PO-PO-PO; EO-PO-PO-PO;

PO-EO-PO; EO-EO-EO-PO; EO-PO-EO-PO;

EO-PO-PO-EO; PO-EO-EO-PO

In the above examples, "n" in the main formula would be an integer offrom 1-4. Since "n" is defined as being from 1 to 12, an even largernumber of possible polyether moieties is included. However, it has beenfound that generally the polyether polyamino methylene phosphonates oflower molecular weight, i.e., where "n" is a smaller integer, are thosewhich provide the greatest amount of scale inhibition under the severeconditions of high pH and high calcite concentration, and thus are thosewhich are preferred. Examples of some of these preferred phosphonatesare shown in the table below, where Z=methylenephosphonate:

    ______________________________________                                         ##STR8##                                                                     Id. No. a          b     R.sub.z  R.sub.a                                                                            R.sub.b                                ______________________________________                                        A       2          1     CH.sub.3 H    CH.sub.3                               B         2.6*     0     CH.sub.3 CH.sub.3                                                                           --                                     C       2          0     CH.sub.3 CH.sub.3                                                                           --                                     D         8.5*     1     CH.sub.3 H    CH.sub.3                               E         5.6*     0     CH.sub.3 CH.sub.3                                                                           --                                     F       2          0     H        H    --                                     G       3          0     H        H    --                                     H       3          0     CH.sub.3 CH.sub.3                                                                           --                                     I       3          1     H        CH.sub.3                                                                           H                                      J       4          0     H        CH.sub.3                                                                           --                                     ______________________________________                                         * = the value of "n" on average.                                         

It will be noted from the table above that in several cases, "n" has anaverage value, i.e., the number of repeating ethyleneoxy or propyleneoxyunits may vary. Thus, it is possible to have a mixture of varying chainlengths of polyoxyethylene or polyoxypropylene in the final product.This is also contemplated to be within the scope of the presentinvention, so long as the requirements with respect to the limit of "n"are observed. Consequently, while "n" is merely defined as an integer orfractional integer which is, or on average is, from about 2 to 12, ithas two aspects. It defines the total of the number of repeatingethyleneoxy and/or propyleneoxy units considered separately, and thus if"n" is, e.g., 4, it includes 4 propyleneoxy units, 3 propyleneoxy unitsand 1 ethyleneoxy units, 2 propylenoxy units and 2 ethyleneoxy units,and so forth. The value of "n" may also represent an average number, andthis is always the case, of course, when it is a fractional integer. Inthis case, for each of the ethylenoxy and/or propyleneoxy unitsconsidered separately, mixtures of these units may be present so as togive an average value for "n". For example, in the table above, for Id.No. D, the total of "a" and "b" is 9.5, which is the value of "n". Whatis described is a mixture of polyether phosphonates in which all of themhave an isopropyl bridging group and an ethyleneoxy moiety, but therepeating propyleneoxy units are such that on average their value isabout 8.5.

The number of repeating ethyleneoxy or oxypropylene units, designated bythe subscript "n", determines the total molecular weight of theoverall(A) polyether polyamino methylene phosphonate, and thus plays acritical role in determining the scale inhibiting performance of thatphosphonate. It has been found that in order to provide adequate scalecontrol using the synergistic combination of the present invention underthe severe conditions of use defined herein, it is necessary that forthe (A) polyether polyamino methylene phosphonate "n" be an integer orfractional integer which is, or on average is, from about 2 to about 12,inclusive.

As discussed above, the reason for "n" being potentially a fractionalinteger arises from the fact that the primary diamine from which thepolyether polyamino methylene phosphonates are prepared byphosphonomethylation may be a mixture of polyethers in which "n" is twoor more of 2, 3, 4, 5 and so forth, in varying proportions. For example,a preferred polyether polyamino methylene phosphonate for use in theaqueous system and methods of the present invention has a molecularweight of approximately 632 and the value of "n" on average is about2.6. Thus, this type of polyether phosphonate has a molecular weightdistribution, i.e., of the various polyoxypropylenes which make it up,and this distribution is represented by a fractional integer averagevalue for "n". But, it is also within the scope of the present inventionfor "n" to be a whole integer, e.g., "3", which usually designates asingle molecular weight and not a molecular weight distribution.

The (A) polyether polyamino methylene phosphonates of the synergisticcombination of the aqueous system and methods of the present inventionare prepared first by phosphonomethylation of the appropriate primarydiamine which already contains the polyoxyethylene and polyoxypropylenemoieties.

Such primary amine starting materials and their method of preparationare well known. The phosphonomethylation of the primary diamine is thencarried out by a Mannich reaction such as that described in K.Moedritzer and R. Irani, J. Organic Chem. 31(5) 1603-7, "The DirectSynthesis of alpha-Aminomethyl Phosphonic Acids; Mannich-Type Reactionswith Orthophosphorous Acid", May 1966. In a typical reaction, theprimary diamine is added to a mixture of phosphorous acid and water, andconcentrated hydrochloric acid is then added slowly, after which thereaction mixture is heated to reflux with addition of aqueousformaldehyde.

Although the general structural formula employed herein indicates thatthe nitrogen atom is completely phosphonomethylated, as a practicalmatter, preparation of the polyether polyamino methylene phosphonates ofthe present invention, as described in detail further below, usuallyresults in only about 80 to 90% phosphonomethylation. Other sideproducts give N-substitution with H, CH₃, CH₂ OH, etc. It is notpractical, as a matter of simple production economics, however, toisolate and purify the completely phosphonomethylated compounds, sincethe side products just described do not interfere with scale depositinhibition. Such side products, are consequently, usually allowed toremain, and the test data set out further below is based on test samplescontaining such side products. Consequently, the activity levelsobtained would be even higher were 100% active compound being tested.

Preparation of the preferred (A) polyether polyamino methylenephosphonate, N,N,N',N'-tetramethylene phosphono polyoxypropylenediamine, is set forth below.

A diamine having an average molecular weight of about 230 and having thestructural formula: H₂ NCH(CH₃)--CH₂ -- --OCH₂ CH(CH₃)--!₂.6 --NH₂ (56.2g) was added to a mixture of phosphorous acid (82 g) and deionized water(65 g) in a one liter resin flask fitted with a condenser, a Teflon®(DuPont) stirrer, a thermometer and an addition funnel. It is importantto maintain as low a level of iron (Fe) in the reaction mixture aspossible, and the most likely source of Fe is the phosphorous acid. TheFe interferes somewhat with the reaction, and consequently a low Fecontent phosphorous acid is employed.

There was then added slowly to the reaction mixture 50 mL ofconcentrated HCl. The reaction mixture was subsequently heated to reflux(107° C.). The temperature should be at least 95° C., but the bestresults are obtained when the reaction mixture is heated to reflux.After the reaction mixture reached reflux, there was added 150 g of 37%aqueous HCHO, which was added dropwise over a period of about 45 min. Inorder to obtain the best results, the ratio of HCHO to diamine startingmaterial should be at least 4:1 on a molar basis, and preferablysomewhat higher, as was the case in this synthesis.

The reaction mixture was then refluxed for an additional period of 3hrs. While the reaction time depends upon temperature, best results areobtained by refluxing for at least 1/2 hr., preferably 2 to 3 hrs.

The reaction mixture was then cooled, and 97.2 g of volatiles werestripped off at 50° C. using a rotary evaporator. A total of 303.4 g ofproduct was obtained, with a theoretical activity of 48%. P₃₁ NMRindicated that at least about 85% of the --NH groups has beenphosphonomethylated. Impurities included unreacted phosphorous acid,formaldehyde, phosphoric acid, methanolphosphonic acid, and otherunidentified phosphorous compounds.

It has been found that the scale control performance of the polyetherpolyamino methylene phosphonates of the present invention depends tosome extent, although not a very significant extent, on the variationsin the process parameters described above. Best results are obtained,consequently, by employing the optimum conditions as outlined above.

When any of the (A) polyether polyamino methylene phosphonates of thepresent invention are used as described in the synergistic combinationto inhibit the precipitation deposition, deposition, and adherence ofscale-forming salts in the aqueous system, they can be effectivelyemployed for that purpose when added in amounts sufficient to establisha concentration in the aqueous system of from about 1 to 100 mg/L.Preferably, the amount added will be sufficient to establish aconcentration of at least about 6.0 mg/L when the aqueous system has acalcite saturation level of at least 150× as described herein. It isunderstood, however, that many factors, of the type which have beenexplained in detail with regard to the background to the presentinvention, will determine the actual amount of the polyether polyaminomethylene phosphonate compositions of the synergistic combination of thepresent invention which will be added to any particular aqueous systemin order to achieve the maximum amount of inhibition of alkaline earthmetal, particularly, for example, calcium carbonate scale and calciumphosphate scale formation, deposition and adherence in that aqueoussystem. The calculation of those amounts is well within the skill of theartisan skilled in this art.

The (B) terpolymer component of the synergistic combination of theaqueous system comprises the monomers of acrylic acid,sulfophenomethallyl ether and maleic acid. The weight average molecularweight for this terpolymer is in the range from about 4,000 to 10,000.

In a preferred embodiment of the aqueous system of the presentinvention, the synergistic combination as described herein includeswherein the (B) terpolymer is about 84 weight average molecular weightpercent acrylic acid, about 8 weight average molecular weight percentsulfophenomethallyl ether, and about 8 weight average molecular weightpercent maleic acid.

The terpolymer (B) as described herein is present in the aqueous systemas described herein, to establish a concentration of at least about 2.0mg/L, and preferably from about 2.0 mg/L to about 50 mg/L. Morepreferably, the terpolymer (B) is present in the aqueous system toestablish a concentration of at least about 4.0 mg/L, and mostpreferably from about 4 mg/L to 25 mg/L.

The terpolymer (B) described herein may be prepared by conventionalmethods known by those skilled in the art, and is commercially availablefrom Alco Chemical, Chattanooga, Tenn., U.S.A. as "AR540" composition."AR540" is a trademark of Alco Chemical.

For example, the (B) terpolymer, as described herein may be prepared byslowly adding acrylic acid monomer to an aqueous mixture containingmaleic acid and sulfophenomethallyl ether. The aqueous mixture furthercontains an initiator, such as, for example, either sodium hypophosphiteor sodium persulfate. The aqueous mixture is then refluxed for severalhours from about 90° to 105° Centigrade. The molecular weight may becontrolled by adding a chain terminator such as, for example, mercaptanor ispropranol. Thereafter, a caustic such as, for example, an ammoniumsalt may be added to partially neutralize the acid. It is within theskill of those skilled in the art to employ sufficient amounts of theabove starting materials to prepare the (B) terpolymer, as describedherein, of the instant invention.

The (C) hydroxyphosphonoacetic acid component of the synergisticcombination of the aqueous system, as described herein, is present inthe aqueous system to establish a concentration of at least about 1.0mg/L, preferably from about 1.0 mg/L to 15 mg/L, and more preferablyfrom about 2 mg/L to 10 mg/L. The hydroxyphosphonoacetic acid (C) may beprepared by conventional methods known by those skilled in the art, andis commercially available from FMC Corporation, Princeton, N.J. as"Belcor 575" composition. "Belcor 575" is a trademark of FMCCorporation.

For example, the (C) hydroxyphosphonoacetic acid, as described herein,is prepared by reacting sodium hypophosphite with glyoxylic acid orpyruvic acid, respectively, in an aqueous medium, such as, for example,distilled water. The reaction is carried out at elevated temperature,such as, for example, from about 60° to 110° Centigrade in the aqueousreaction medium, under reflux conditions. The reaction is held at thisreflux temperature and the progress of the reaction is monitored by P³¹NMR analysis. The reaction is stopped after 9 hours. It is within theskill of those skilled in the art to employ sufficient amounts of theabove starting materials to prepare the (C) hydroxyphosphonoacetic acid,as described herein, of the present invention.

In a preferred embodiment of the aqueous system of the presentinvention, as described herein, the weight ratio of the combination asdescribed herein, comprising (A) polyether polyamino methylenephosphonate:(B) terpolymer: (C) hydroxyphosphonoacetic acid ranges fromabout 1:2:1 to about 5:2:1.

Thus, it will be appreciated by those skilled in the art that thesynergistic combination (A), (B), and (C) of the aqueous system of thepresent invention can increase the amount of scale control and depositcontrol achieved under the severe conditions described herein moreeconomically than was previously achieved heretobefore.

In addition to the synergistic combination of (A), (B), and (C) of theaqueous system, described herein, other additives may be used in furthercombination which increases the effectiveness of the synergisticcombination (A), (B), and (C) as described herein. Thus, it is desirableto use one or more corrosion inhibitors along with the synergisticcombination of the present invention in order to obtain corrosion rateswhich are acceptable. These corrosion inhibitors, as further describedherein, may be steel and/or copper corrosion inhibitors. Acceptablecorrosion rates depend on the circumstances surrounding each particularuse environment, but will usually depend to a large degree onexpectations with regard to the life expectancy of the equipment presentin said environment. Also, acceptable corrosion almost always implies anabsence of pitting attack type corrosion. The nature of the equipmentinvolved will depend on the application area, but usually the metalsfrom which such equipment is constructed and which are subject tocorrosive attack are, for example, steel in its various common forms,including stainless steel, and copper itself or various alloys thereof,particularly brass. All of these metals are subject to corrosive attack,which, under the severe conditions of use of the aqueous systems andmethods of the present invention, may be even greater than the extent ofcorrosive attack that is experienced under more normal conditions; and,therefore, all of these metals, therefore, will benefit from the use ofone or more corrosion inhibitors in conjunction with the synergisticcombination (A), (B), and (C) of the present invention.

With regard to corrosion inhibitors for steel and its alloys, it hasbeen found that, surprisingly, not all corrosion inhibitors, includingthose which perform well with known phosphonate scale inhibitors used inthe prior art, and might, therefore, be expected to provide adequateprotection, are suitable for use with the synergistic combination of theaqueous system of the present invention. For example, it has been foundthat the molybdate and nitrite classes of corrosion inhibitors, whichusually provide good corrosion protection, especially against pittingattack type corrosion, are not suitable for use with the (A) polyetherpolyamino methylene phosphonate of the synergistic combination of thepresent invention.

On the other hand, there are numerous steel corrosion inhibitors whichare suitable, and such suitability can be readily determined by thoseskilled in the art. Thus it is within the ordinary skill of the artisanto determine which steel corrosion inhibitors would be suitable, and allsuch inhibitors are contemplated to be a part of the present invention.Having carried out the test procedures referred to above, it has beendetermined that one of the following steel corrosion inhibitors provideadequate levels of corrosion protection, including protection againstpitting attack type corrosion, when used in combination with thesynergistic combination of the aqueous system of the present invention:

hexametaphosphate,

orthophosphate,

pyrophosphate,

2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC),

manganese Mn(II)⁺² !, and

zinc Zn(II)⁺² !.

The concentration of the steel corrosion inhibitor(s) which is requiredto provide adequate protection against corrosion will depend on themakeup of the water in the aqueous system being treated, the pH, and thetemperature. Generally, however, the desired concentration of thepreferred inhibitors recited above will be in the range of from about0.1 mg/L to about 100 mg/L, preferably from about 1 mg/L to about 25mg/L, and most preferably from about 1 mg/L to about 10 mg/L.

With regard to corrosion inhibitors for copper and its alloys, againthose skilled in the art can readily determine which copper corrosioninhibitors are suitable. For example, following are suitable coppercorrosion inhibitors for use with the aqueous system described herein ofthe present invention:

benzotriazole,

tolyltriazole,

2-mercaptobenzothiazole,

combinations of tolyltriazole and mercaptobenzothiazole as described inU.S. Pat. No. 4,675,158,

higher alkylbenzotriazoles of the type described in EP-A-0 397 454, andcombinations thereof as described in EP-A-0 462 809,

alkoxybenzotriazoles and combinations thereof as described in EP-A-0 478247, and

phenyl mercaptotetrazole and combinations thereof as described in EP-A-0462 666.

The concentration of the desired copper corrosion inhibitor which shouldbe used will depend not only on the inhibitor itself, but on suchfactors as the yellow metal surface area and total aqueous systemvolume, the concentration of dissolved and suspended copper, the pH,dissolved solids, and temperature. Generally, however, suitable coppercorrosion inhibitors will be added in a range of concentrations fromabout 0.1 to about 100 mg/L, preferably from about 0.5 to about 20 mg/Land most preferably from about 1 to about 5 mg/L.

Further, it will be appreciated by those skilled in the art, that otheradditives may be added to the synergistic combination of the aqueoussystem, such as for example, a stabilizer for preventing decompositionof component (A) polyether polyamino methylene phosphonate of thesynergistic combination of the aqueous system of the present invention.It will be understood by those skilled in the art that decomposition ofdeposit control agents may occur, for example, in the presence ofbiocide compositions containing, for example, chlorine, bromine ormixtures thereof. It is also known by those persons skilled in the artthat aqueous systems commonly contain biocide compositions for biologiccontrol. Examples of a suitable stabilizer that may be added to theaqueous system of the present invention include, but are not limited to,monoethanolamine and an organic sulfonamide comprising the compound ofthe formula ##STR9## wherein: Z is selected from hydrogen; and alkaliand alkaline earth metal salt-forming ions; and

R is selected from the group consisting essentially of:

a) C₁₋₄ alkoxy radical: --OC₁₋₄ alkyl;

b) an amino group, or a mono(C₁₋₄ alkyl)amino or di(C₁₋₄ alkyl)aminogroup: --N(R¹)R², where R¹ and R² are as defined above;

c) a formylamino group: --NHC(O)H;

d) (C₁₋₄ alkyl) carbonylamino radical: --NH--C(O)C₁₋₄ alkyl;

e) (C₁₋₄ alkoxy) carboylamino radical: --NH--C(O)OC₁₋₄ alkyl;

f) C₂₋₆ alkenyl radical;

g) C₂₋₆ alkynyl radical;

h) C₃₋₇ cycloalkyl radical;

i) aryl or heteroaryl selected from the group consisting essentially ofphenyl, naphthyl, pyridyl, pyrimidyl, pyrazyl, pyridazyl, pyrrolyl;imidazolyl, pyrazolyl, triazolyl, tetrazolyl; wherein the aryl andcarbon atoms of the heteroaryl are optionally substituted with up tothree radicals selected from the group consisting essentially of: C₁₋₄alkyl, C₁₋₄ alkoxy, C₁₋₄ alkoxycarbonyl; halo; nitro; nitrillo; carboxy;C₁₋₄ alkylsulfonyl radical: --S(O)_(n) C₁₋₄ alkyl, where n=2; and asulfamolyl group which is unsubstituted or substituted on the nitrogenby one or two C₁₋₄ alkyl group: SO₂ N(R¹)R², where R¹ and R² are asdefined above; and wherein the nitrogen atom(s) of the heteroaryl is(are) optionally substituted by C₁₋₄ alkyl of C₁₋₄ alkylsulfonylradical: --S(O)_(n) C₁₋₄ alkyl, where n=2;

j) C₁₋₄ alkyl radical; and

k) C₁₋₄ alkyl monosubstituted by one of the substituents a) through i)above.

Preferred organic sulfonamide stabilizing agents for use in the presentinvention are those set out above wherein R is:

C₁₋₄ alkoxy radical: --OC₁₋₄ alkyl;

an amino group, or a mono(C₁₋₄ alkyl)amino or

di(C₁₋₄ alkyl)amino group: --N(R¹)R², where R¹ and R² are independentlyH or C₁₋₄ alkyl;

phenyl mono-substituted by C₁₋₄ alkyl, C₁₋₄ alkoxy, or --SO₂ N(R¹)R²,where R¹ and R² are as defined above; C₁₋₄ alkyl radical; or C₁₋₄ alkylmonosubstituted by one of the substituents set out immediately above.

An especially preferred class of organic sulfonamides useful in thepresent invention is that wherein R is phenyl monosubstituted by C₁₋₄alkyl, and more particularly, para-substituted by methyl.

The organic sulfonamides described above are, for the most part, knownin the art, and methods for their preparation are well known. Onesatisfactory approach to preparation of these compounds is bysulfonation of the appropriate amine with sulfur trioxide: SO₃. Anothersynthetic approach which may be used to prepare the organic sulfonamidestabilizers of the present invention is by treating ammonia, a primaryamine, or a secondary amine with a sulfonyl chloride in the presence ofsome base. These and other methods are described in ComprehensiveOrganic Chemistry: the Synthesis and Reactions of Organic Compounds,Vol. 3, pp. 345-346, Derek Barton and W. David Ollis, eds., PergamonPress 1979, as well as the literature references cited therein.

The overall amount, and particularly the concentration of organicsulfonamide stabilizing agent which must be employed in the aqueoussystem and methods of the present invention for inhibiting thedegradation of the (A) polyether polyamino methylene phosphonate of thesynergistic combination of the present invention depends on a number offactors, including especially pH, concentration of the chlorine and/orbromine biocide, and temperature and organic and inorganic constituentsof the water which makes up the aqueous system being treated. Withregard particularly to the concentration of the chlorine and/or brominebiocide in the aqueous system, it is desirable that the correspondingconcentration of the organic sulfonamides stabilizing agent be in anequivalent weight ratio thereto (sulfonamide:halogen) of from about 0.5to 2.0, preferably from about 0.75 to 1.25, and most preferably about1.0. In general terms, the concentration of the organic sulfonamide willbe from 0.1 to 100 ppm, preferably from 0.5 to 25, most preferably from1 to 10 ppm in the aqueous system being treated by the synergisticcombination (A), (B) and (C) of the present invention. For example, theorganic sulfonamide stabilizing agents of the present invention will beadded to the aqueous system at a concentration of between 0.5 and 25ppm, wherein the aqueous system is at a pH of from 6 to 10, at atemperature of from 10° to 80° C. (Centigrade), and having a chlorineand/or bromine concentration of between about 0.1 and 50 ppm, andusually from about 0.1 to 10 ppm.

In another embodiment of the present invention, a method is provided forinhibiting the formation deposition and adherence of scale forming saltsin an aqueous system having a pH of at least 8.5 and a calcitesaturation level of at least 100 times the solubility limit of calciumas calcite, comprising adding to said aqueous system an effective amountof combination of (A) an amount to establish a concentration of at leastabout 1.0 mg/L of a polyether polyamino methylene phosphonate of theformula: ##STR10## where n is an integer or fractional integer which is,or on average is, from about 2 to about 12, inclusive; M is hydrogen ora cation of an alkali metal salt; and each R may be the same ordifferent and is independently selected from hydrogen and methyl; adding(B) an amount sufficient to establish a concentration of at least about2.0 mg/L of a terpolymer comprising the monomers of acrylic acid,sulfophenomethallyl ether and maleic acid, wherein said terpolymer has aweight average molecular weight in the range from about 4,000 to 10,000;and adding (C) an amount sufficient to establish a concentration of atleast about 1.0 mg/L of a hydroxyphosphonoacetic acid. Preferably thismethod includes wherein for the polyether polyamino methylenephosphonate, as described herein, M is hydrogen, each R is methyl, and nis from about 2 to 4, and more preferably wherein n is about 2.6.

In another embodiment of the method of the present invention, a methodis provided wherein the terpolymer (B) is about 84 weight averagemolecular weight percent acrylic acid, about 8 weight average molecularweight sulfophenomethallyl ether, and about 8 weight average molecularweight percent maleic acid.

Preferably the method of the invention, as described herein, includeswherein the ratio of (A):(B):(C) of the synergistic combination of theaqueous system ranges from about 1:2:1 to about 5:2:1.

In a most preferred embodiment of the method of this invention, asdescribed herein, the method provides from adding the synergisticcombination (A), (B) and (C) to the aqueous system having a calcitesaturation level of at least 150 times the solubility limit of calciumas calcite wherein the (A) polyether polyamino methylene phosphonate ispresent in a concentration of at least about 6.0 mg/L, the (B)terpolymer is present in a concentration of at least about 4.0 mg/L, andthe (C) hydroxyphosphonoacetic acid is present in a concentration of atleast about 2.5 mg/L.

Another embodiment of the present invention includes the method, asdescribed herein, that further includes adding a stabilizer, asdescribed hereinbefore, to the aqueous system for preventingdecomposition of the synergistic combination, and more particularly forpreventing the decomposition of the polyether polyamino methylenephosphonate (A).

Another embodiment of the present invention provides for a method, asdescribed herein, that further includes adding at least one corrosioninhibitor, as described hereinbefore. More preferably this methodincludes adding the corrosion inhibitor wherein it is a copper corrosioninhibitor and most preferably wherein the copper corrosion inhibitor istolyltriazole.

The manner of addition of each component of the synergistic combination,and the other additives such as for example, the copper corrosioninhibitor, the steel corrosion inhibitor, and/or the stabilizer, asdescribed herein, to the aqueous system of the present invention will bestraightforward to a person of ordinary skill in the art. Each componentof the synergistic combination may be added singularly or in anycombination with each other. The order of addition of (A), (B) and (C)of the synergistic combination to the aqueous system of the presentinvention is not important. Similarly, the addition of the corrosioninhibitor(s), and/or stabilizer(s) to the aqueous system of thisinvention may be accomplished singularly or in combination with eachother, and the order of addition is not critical relative to thecomponents of the synergistic combination (A), (B) and (C) of thisinvention. Thus, it will be appreciated by those skilled in the art thatthe addition of the hereinbefore mentioned components of the synergisticcombination (A), (B) and (C) and the hereinbefore mentioned additivesmay be accomplished by adding each of (A), (B), (C), corrosioninhibitor(s), or stabilizer(s), individually as a single additive to theaqueous system, or in any combination of two or more of the following(A), (B), (C), corrosion inhibitor or stabilizer to achieve the aqueoussystem of the present invention that includes at least (A), (B) and (C)as described herein to establish the synergistic effect taught by thisinvention.

Further, the manner of addition of the components (A), (B) and (C),and/or stabilizer(s), and/or corrosion inhibitor(s) of the presentinvention is straightforward to a person of ordinary skill in the art.Each of the components may be added in liquid form by mechanicaldispensers of known design. They may also be added in diluted liquidform. As discussed hereinbefore, for example, two or more components maybe combined for dispensing to the aqueous system; and these incombination may be dispensed in liquid form.

EXAMPLES

The following examples demonstrate the invention in greater detail.These examples are not intended to limit the scope of the invention inany way. In the examples the following products were used:

TRC is a polyether polyamino methylene phosphonate (A), as set forth inthe formula described hereinbefore, wherein both R's are methyl, M ishydrogen, n is on average 2.6 and the resultant weight average molecularweight is about 600. TRC is commercially available for use in theaqueous system, as described herein, from Calgon Corporation,Pittsburgh, Pa., U.S.A. Belcor 575 is hydroxyphosphonoacetic acid and iscommercially available from FMC Corporation, Princeton, N.J., U.S.A.

AR540 is a terpolymer comprising about 84 weight average molecularweight percent acrylic acid, about 8 weight average molecular weightpercent sulfophenomethallyl ether, and about 8 weight average molecularweight percent maleic acid. AR540 is commercially available from AlcoChemical, Chattanooga, Tenn., U.S.A.

Examples 1-14

In Examples 1-14 various formulations were tested for theireffectiveness in improving the inhibition of the formation, depositionand adherence of calcium carbonate (CaCO₃) and calcium phosphate (CaPO₄)at pH 8.5, and calcite saturation at about 100 times the solubilitylimit of calcium as calcite. In order to demonstrate the improved scaleinhibitor performance of the aqueous system of the present invention,the following procedure was used: Scaling water containing 150 mg/L ofCa⁺² and 600 mg/L of alkalinity as calcium carbonate and about 2 mg/L oforthophosphate at a pH of about 8.5 and 60° Centigrade to achieve acalcite saturation of about 100× was used to evaluate scale inhibitionperformance of test solutions (Examples 1-14) over a 24 hour period.Test solutions were analyzed by withdrawing 10 grams of test solutionand adding to it an appropriate container through a 0.2 micron filterand titrating for calcium by the Schwarzenbach method and PO₄ ³ by usingthe spectrophotometric method known by those skilled in the art, andcalculating the percent inhibition by methods known by those skilled inthe art. The make-up of the test solutions of each example is set forthin Table 1. Table 1 also shows the results of the above scale inhibitingactivity evaluations over a time period of 24 hours, wherein the percent(%) inhibition of calcium carbonate (CaCO₃) and calcium phosphate(CaPO₄) was calculated at 24 hours for each example.

                  TABLE 1                                                         ______________________________________                                        AR540,       Belcor-575,                                                                             TRC     % Inhibition                                   Example mg/L     mg/L      mg/L  CaCO.sub.3                                                                           CaPO.sub.4                            ______________________________________                                        1       2        --        --    37     69                                    2       2        --        --    35     72                                    3       --       1         --    40     17                                    4       2        --        1     92     89                                    5       2        1         --    53     80                                    6       --       1         1     100    50                                    7       2        1         1     100    100                                   8       --       --        6     100    42                                    9       --       --        25    100    100                                   10      4        --        --    69     100                                   11      --       2.5       --    61     27                                    12      4        --        6     100    100                                   13      4        2.5       --    76     100                                   14      --       2.5       6     100    44                                    ______________________________________                                    

Examples 1 through 3, Table 1, show that each component of thesynergistic combination of the aqueous system of the present inventionwhen used individually in an aqueous system having scaling watercontaining 150 mg/L Ca⁺², 600 mg/L of alkalinity as calcium carbonateand about 2 mg/L orthophosphate at a pH of about 8.5, as describedhereinbefore, do not achieve sufficient inhibition of calcium carbonateand calcium phosphate scale at a calcite saturation at about 100 times(100×) the solubility limit of calcium as calcite.

Examples 4 through 6 show that when a combination of any two componentsof the synergistic combination of the present invention are usedtogether, inhibition of both calcium carbonate and calcium phosphate isnot achieved. Example 7 shows that the synergistic combination of thepresent invention wherein 1 mg/L of TRC (polyether polyamino methylenephosphonate (A) of the formula, as described herein), 1 mg/L of Belcor575 (hydroxyphosphonoacetic acid), and 2mg/L AR540 (terpolymer asdescribed herein) effectively inhibits 100% of the formation of bothcalcium carbonate and calcium phosphate scales.

Examples 8, 10 and 11 show that increasing the concentration ofemploying a single component alone of the synergistic combination of thepresent invention does not achieve sufficient inhibition of both calciumcarbonate and calcium phosphate scale formation. Example 9 shows thatuse of TRC alone at a concentration of 25 mg/L inhibits 100% of bothcalcium phosphate and calcium carbonate scales, however, achieving aconcentration of at least 25 mg/L of TRC is expensive, and thus adisadvantage to improving the operating costs of the process using theaqueous system with TRC alone.

Example 12 shows that employing a concentration of 4 mg/L of AR540 and 6mg/L of TRC effectively inhibits 100% of the formation of calciumcarbonate and calcium phosphate scale. While the synergistic combinationset forth in Example 12 effectively inhibits the scale formation, it isless economical to employ in a process having the aqueous system of thepresent invention when compared to the synergistic combination of thepresent invention described in Example 7.

Examples 13 and 14 show that employing higher concentrations of either acombination of AR540 and Belcor-575, or a combination of Belcor-575 andTRC do not achieve sufficient inhibition of both the formation ofcalcium carbonate and calcium phosphate scales in the aqueous system.

Examples 15-22

In Examples 15 through 22, various formulations were tested for theireffectiveness in improving the inhibitor of the formation, depositionand adherence of calcium carbonate and calcium phosphate. In order todemonstrate the improved scale inhibition performance of the aqueoussystem of the present invention, the following procedure was used:

Scaling water containing 150 mg/l of Ca⁺² and 600 mg/L of alkalinity ascalcium carbonate and about 2 mg/L of orthophosphate at pH of about 8.8and 60° Centigrade to achieve a calcite saturation of about 150× wasused to evaluate scale inhibition performance of test solutions(Examples 15-22) over a 24 hour period. Test solutions were analyzed bywithdrawing 10 grams of test solution and adding it to an appropriatecontainer through a 0.2 micron filter and titrating for calcium by theSchwarzenbach method and PO₄ ³⁻ by using the spectrophotometric methodknown by those skilled in the art and calculating the percent inhibitionby methods known by those skilled in the art. The make-up of the testsolutions of each example (Examples 7-22) is set forth in Table 2. Table2 also shows the results of the above scale inhibitor activityevaluations over a time period of 24 hours, wherein the percent (%)inhibition of calcium carbonate and calcium phosphate was calculated at24 hours for each example.

                  TABLE 2                                                         ______________________________________                                        AR540,       Belcor-575,                                                                             TRC     % Inhibition                                   Example mg/L     mg/L      mg/L  CaCO.sub.3                                                                           CaPO.sub.4                            ______________________________________                                        15      --       --        6     87     27                                    16      4        --        --    60     49                                    17      --       2.5       --    69     29                                    18      4        --        6     89     80                                    19      4        2.5       --    80     39                                    20      --       2.5       6     97     11                                    21      2        1         1     65     45                                    22      4        2.5       6     100    100                                   ______________________________________                                    

Table 2 shows the results obtained for various formulations' abilitiesto inhibit the formation of calcium carbonate and calcium phosphatescales in an aqueous system having a pH of at least about 8.5 and acalcite saturation of at least 150 times the solubility limit of calciumas calcite (150×).

Examples 15-17 and Examples 18-20 of Table 2 demonstrate that when asingle component of the synergistic combination of the aqueous system ofthe instant invention is employed alone, or a combination employing anytwo components of the synergistic combination of this invention,respectively, are employed in the aqueous system having a calcitesaturation of 150×, effective inhibition of both calcium carbonate andcalcium phosphate scales are not achieved.

Examples 21 and 22, Table 2, show that a concentration of at least a 4mg/L AR540, 2.5 mg/L Belcor-575, and 6 mg/L TRC of the synergisticcombination of the aqueous system of the present invention is requiredto inhibit 100% of both calcium carbonate and calcium phosphate scalesin an aqueous system having a calcite saturation of at least 150×.

Examples 23-24

In Examples 23 and 24, formulations were tested for effectiveness inproviding 100% deposit control for both calcium carbonate and calciumphosphate and for providing protection against corrosion in scalingwater containing 200 mg/L of Ca²⁺ and about 4 mg/L of orthophosphate atpH of about 8.5 and 60° C. to achieve a calcite saturation at about 240times the solubility limit of calcium as calcite. The analysis methodset forth herein under Examples 1-14 was then followed. The makeup ofthe formulation for Example 23 contained about 8 mg/L TRC, and themakeup of the formulation for Example 24, an example of the synergisticcombination of the instant invention, contained about 8 mg/L TRC, 6 mg/Lof component (B) of the instant invention, 4 mg/L of component (C) ofthe instant invention, 5 mg/L of the stabilizer monethanolamine, and 2mg/L of the copper corrosion inhibitor tolyltriazole.

Corrosion test procedures were carried out in an 8 L vessel fitted witha heater having a temperature controller, a pump to circulate the waterin the test apparatus, a pH monitor and controller to maintain thedesired pH, and an aerator to both ensure air saturation, and tointroduce carbon dioxide gas as required for pH control. The steelcoupon specimens for the test were composed of 1010 carbon steel (UNSdesignation G10100), and these were immersed in the water of the testapparatus. Corrosion penetration rates in mils per year (mpy) weredetermined gravimetrically after 7 days by the standard ASTM-G1-88method. The composition of the water used in the test apparatus was asfollows:

    ______________________________________                                        Ion           Conc. (mg/L)                                                    ______________________________________                                        Ca            200                                                             Mg            40                                                              Cl            416                                                             SO.sub.4      1025                                                            SiO.sub.2     14                                                              Alkalinity as 498                                                             CaCO.sub.3                                                                    ______________________________________                                    

Table 3 shows the results of the scale deposit evaluation over a timeperiod of 24 hours wherein the percent (%) inhibition of calciumcarbonate and calcium phosphate was calculated at 24 hours for eachexample.

                  TABLE 3                                                         ______________________________________                                                  Deposit Control                                                               as % Inhibition                                                                           Corrosion                                               Example   CaCO.sub.3  CaPO.sub.4                                                                            Rate (mpy)                                      ______________________________________                                        23         80          80     15                                              24        100         100     0.7                                             ______________________________________                                    

It will be appreciated by those skilled in the art that the data ofTable 3 demonstrates that the aqueous system containing the synergisticcombination as disclosed by the instant invention provides a dramaticimprovement in corrosion rate over treatment known in the art.

From the above data, it will be appreciated by those skilled in the artthat the methods and aqueous system of the present invention comprisingthe synergistic combination of the (A) polyether polyamino methylenephosphonate, as described herein, the (B) terpolymer, as describedherein, and the(C) hydroxyphosphonoacetic acid, as described herein,significantly improve the inhibition of both calcium carbonate andcalcium phosphate scales in an aqueous system having a calcitesaturation level of at least 100 times the solubility limit of calciumas calcite, over conventional known compositions. Further, the presentinvention provides an economical resolution to the problem of inhibiting100 percent of both calcium carbonate and calcium phosphate scaleformation in an aqueous system not heretobefore possible.

Whereas particular embodiments of the instant invention have beendescribed for the purposes of illustration, it will be evident to thoseskilled in the art that numerous variations and details of the instantinvention may be made without departing from the instant invention asdefined in the appended claims.

What is claimed is:
 1. An aqueous system containing scale forming saltsand wherein the pH of said system is at least 8.5 and the calcitesaturation of said system level is at least 100 times the solubilitylimit of calcium as calcite, which further contains a synergisticeffective amount of a combination comprising: (A) a polyether polyaminomethylene phosphonate of the formula: ##STR11## where n is, or onaverage is, from about 2 to about 12, inclusive; M is hydrogen or acation of an alkali metal salt; and each R may be the same or differentand is independently selected from hydrogen and methyl; (B) a terpolymercomprising the monomers of acrylic acid, sulfophenomethallyl ether andmaleic acid, wherein the weight average molecular weight for saidterpolymer is in the range from about 4,000 to 10,000; and (C) ahydroxyphosphonoacetic acid.
 2. The aqueous system of claim 1 whereinfor said polyether polyamino methylene phosphonate, M is hydrogen, eachR is methyl, and n is from about 2 to
 4. 3. The aqueous system of claim2 wherein n is about 2.6.
 4. The aqueous system of claim 3 wherein theaqueous system is a cycled up cooling tower.
 5. The aqueous system ofclaim 1, wherein said terpolymer is about 84 weight average molecularweight percent acrylic acid, about 8 weight average molecular weightpercent sulfophenomethallyl ether, and about 8 weight average molecularweight percent maleic acid.
 6. The aqueous system of claim 1 wherein theweight ratio of A:B:C ranges from about 1:2:1 to about 5:2:1.
 7. Theaqueous system of claim 1 wherein said polyether polyamino methylenephosphonate is present in said aqueous system to establish aconcentration of at least about 1.0 mg/L.
 8. The aqueous system of claim7 wherein said polyether polyamino methylene phosphonate is present insaid aqueous system to establish a concentration of at least about 6.0mg/L.
 9. The aqueous system of claim 1 wherein said terpolymer ispresent in said aqueous system to establish a concentration of at leastabout 2.0 mg/L.
 10. The aqueous system of claim 9 wherein saidterpolymer is present in said aqueous system to establish aconcentration of at least about 4.0 mg/L.
 11. The aqueous system ofclaim 1 wherein said hydroxyphosphonoacetic acid is present in saidaqueous system to establish a concentration of at least about 1.0 mg/L.12. The aqueous system of claim 11 wherein said hydroxyphosphonoaceticacid is present in said aqueous system to establish a concentration ofat least about 2.5 mg/L.
 13. The aqueous system of claim 1 additionallyincluding a stabilizer for preventing decomposition of said polyetherpolyamino methylene phosphonate.
 14. The aqueous system of claim 13wherein said stabilizer is monoethanolamine.
 15. The aqueous system ofclaim 1 additionally including at least one corrosion inhibitor.
 16. Theaqueous system of claim 15 wherein said corrosion inhibitor is a coppercorrosion inhibitor.
 17. The aqueous system of claim 16 wherein saidcopper corrosion inhibitor is tolyltriazole.
 18. The aqueous system ofclaim 15 additionally including a stabilizer for preventingdecomposition of said polyether polyamino methylene phosphonate.